Field of the Invention
The present invention relates to a magnetoresistance effect element. Priority is claimed on Japanese Patent Application No. 2016-192007, filed Sep. 29, 2016, the content of which is incorporated herein by reference.
Description of Related Art
A giant magnetoresistance (GMR) element made of a multilayer film including a ferromagnetic layer and a nonmagnetic layer and a tunnel magnetoresistance (TMR) element in which an insulating layer (a tunnel barrier layer, a barrier layer) is used for the nonmagnetic layer are known. Generally, although a TMR element has a higher element resistance as compared with a GMR element, a TMR element has a larger magnetoresistance (MR) ratio than an MR ratio of a GMR element. Therefore, attention is focused on a TMR element as an element for magnetic sensors, high frequency components, magnetic heads, and magnetic random access memories (MRAMs).
TMR elements can be classified into two types by a difference in mechanism of electron tunnel conduction. One is a TMR element utilizing only a leaking effect (tunnel effect) of a wave function between ferromagnetic layers. The other is a TMR element dominated by a coherent tunnel (only electrons having symmetry of a specific wave function tunnel) utilizing conduction of a specific orbit of the nonmagnetic insulating layer to be tunneled when a tunneling effect occurs. It is known that a TMR element in which a coherent tunnel is dominant can obtain a larger MR ratio as compared with a TMR element using only the tunnel effect.
To obtain the coherent tunnel effect in a magnetoresistance effect element, it is necessary that two ferromagnetic metal layers and a tunnel barrier layer are all crystalline and interfaces between the two ferromagnetic metal layers and the tunnel barrier layer are crystallographically continuous.
MgO is widely known as a tunnel barrier layer capable of obtaining the coherent tunnel effect. Research on materials able to be substituted for MgO is also in progress. For example, in JP5586028B, MgAl2O4 having a spinel structure has been reported as an alternative material to MgO. In addition, JP2013-175615A describes that MgAl2O4 having a disordered spinel structure is used for a tunnel barrier layer.